Unwinding of Globular Polymers under Strong Flows

In poor solvent, a flexible polymer chain ( N monomers) collapses into a globule. When stretched at both ends, it switches from a globular to a stretched form by a first-order transition. When the coil is stretched under a uniform solvent flow at velocity V, we predict that the transition is second order (continuous). We expect three regimes. (i) V < V 1: the globule elongates slightly into an ellipsoid and the resistance is provided by surface tension. (ii) V 1 < V < V 2: we have coexistence between a reduced globule and an extended chain. (iii) V > V 2: the globule has completely faded out. When stretched under a shear flow, we also expect three regimes, but the deformation is now more progressive. In the stem−globule regime, the stem can be either fully elongated or only partially stretched. Finally, we discuss transients, where (i) the chain fully elongated at time t = 0 relaxes to the equilibrium collapsed state and (ii) starting from a globule at rest, a uniform flow is suddenly imposed.